In general, aircraft pneumatic tires are classified into two types: a bias-ply tire having a carcass of a bias structure and a radial tire having a carcass of a radial structure. A bias-ply tire includes, on the outside of a carcass having a bias structure, a cushion rubber layer for protecting the carcass ply from being damaged and one or two crown protective layers composed of diagonally disposed organic fibers, from the inside to the outside. In addition, the bias-ply tire also includes a top tread having circumferential straight grooves.
A radial tire includes a plurality of belt plies on the outside of a carcass having a radial structure. To protect the belt plies from being damaged, a radial tire also includes, on the outside of the belt plies, a cushion rubber layer and a crown protective layer of a corrugated cord layer or one or two crown protective layers composed of diagonally disposed organic fibers, from the inside to the outside. A radial tire further includes a top tread having circumferential straight grooves. In general, an aircraft pneumatic tire is replaced with a new one when grooves in a top tread are lost because of wear.
In existing aircraft pneumatic tires, a top tread having a so-called cap and base structure used in pneumatic tires for passenger cars or trucks/buses is not used. This is because the application of a known base rubber compound to an aircraft pneumatic tire results in inappropriate difference in rigidity from both a crown protective layer and a cap rubber, which causes strain concentration during the deformation of a tread under a high load and at a high speed, where an aircraft pneumatic tire is used, thus increasing the possibility of blowout.
In this situation, Patent Document 1, discloses an aircraft tire having a cap/base tread. Patent Document 1 does not take the difference in rigidity into consideration, the aforementioned problem that strain concentration during the deformation of a tread increases the possibility of blowout remains unsolved. Furthermore, Patent Document 1 does not disclose a region occupied by a base rubber.
Apart from the application in an aircraft, for example, Patent Document 2, describes a technique in which, in a pneumatic tire having a tread composed of at least two rubbers, the relationships in the resilience (rebound resilience), the modulus of elasticity, the tread gage, and the like between a cap tread rubber and a base tread rubber are defined to reduce the amount of heat liberated by the tire without decreasing the durability of belt ends and improve the durability of the tire at the same time. Patent Document 3, describes a radial tire for use in passenger cars in which the resilience of each layer of a tread rubber having a two-layer structure is defined. Patent Document 4 describes an automobile tire in which the relationship between the rebound resilience of a base rubber and the loss modulus of a cap rubber is referred to. Patent Document 5 also describes a pneumatic tire in which the relationship between the resilience of a cap rubber layer and the resilience of a base rubber layer is referred to.
Patent Document 1:, Japanese Unexamined Patent Application Publication No. 2-185806
Patent Document 2:, Japanese Unexamined Patent Application Publication No. 54-38004
Patent Document 3:, Japanese Unexamined Patent Application Publication No. 55-99403
Patent Document 4:, Japanese Unexamined Patent Application Publication No. 56-8704
Patent Document 5:Japanese Unexamined Patent Application Publication No. 6-227211